Twenty-five years ago nearly all physicians believed tuberculosis a hereditary disease. Now nearly everyone considers that heredity plays at most a minor rôle and that the disease is acquired in the great majority of cases. The problem now at issue is how it is acquired. Koch declares that it is practically always due to the inhalation of germs from other human beings who have tuberculosis, while von Behring proclaims quite as confidently that it is due to milk infection.

In a recent article1 von Behring reiterates this statement and insists that practically only such individuals acquire tuberculosis as have had the germs of the disease brought into their bodies with the milk in childhood. These milk bacilli work their way through the digestive organs and lymphatics into the blood and finally, he asserts, the lungs become infected from the blood. "Even such tubercle bacilli as are inhaled with the